1. Field of the Invention
The present invention relates to a swash plate compressor and, more particularly, to an assembly structure of thrust bearings for supporting a swash plate in the axial direction of a drive shaft.
2. Description of the Related Art
A swash plate compressor has a piston fitted reciprocally in a cylinder bore which is formed in a cylinder block. The swash plate is fixed on the drive shaft in a crank chamber which is formed in the cylinder block. When the swash plate is turned according to the rotation of the drive shaft, the piston is reciprocated to effect the suction and compression of a cooling gas in the cylinder bore.
In the compressor disclosed in the Unexamined Japanese Patent Publication No. 62-51776, for example, a compression reaction force is applied to a swash plate 30, as shown in FIG. 1, in response to the reciprocation of the piston. In order to receive this compression reaction force, a pair of ring-shaped elastic thrust bearings 34 are individually sandwiched in slanting positions between the front and rear end portions of a boss 31 of the swash plate 30 and the inner wall faces of a crank chamber 32.
Each of the thrust bearings 34 includes a pair of thrust races 34a and 34b and a set of needles 34c disposed between the races. The inner thrust races 34b are pre-loaded at their outer circumferential sides toward the outer thrust races 34a by means of movable thrust receiving faces 35 of the boss 31. On the other hand, the outer thrust races 34a are pre-loaded at their inner circumferential sides toward the inner thrust races 34b by means of stationary thrust receiving faces 37 of cylinder blocks 36. As a result, the boss 31 of the swash plate 30 is elastically supported and restrained by the paired front and rear thrust bearings 34 so as to have its longitudinal reciprocation restricted by the predetermined load.
In the compressor described above, the movable thrust receiving faces 35 of the swash plate 31 and the stationary thrust receiving faces 37 of the cylinder blocks 36 are positioned at a predetermined spacing from each other. Moreover, the individual thrust receiving faces 35 and 37 are inclined at a predetermined angle .theta.s with respect to a line L which is perpendicular to the axis of a drive shaft 38. After thrust bearings 34 have been assembled, however, the angle contained between the thrust races 34a and 34b and the line L is .theta.m, which is smaller than the angle of inclination .theta.s. As a result, a gap G is established between the individual races of the assembled thrust bearings 34 and the thrust receiving faces 35, 37.
When the swash plate 30 rotates during operation of the compressor, the swash plate 30 is pushed along the axis of the drive shaft 38 by the compression reaction force of the piston. At this time, the two thrust bearings 34 are elastically deformed to cause the front side thrust bearing 34 (as located at the left-hand side of FIG. 2), for example, to contact in a face-to-face manner the stationary thrust receiving face 37, as shown in FIG. 2. Simultaneously with this, the rear side thrust bearing 34 (as located at the right-hand side of FIG. 2) is elastically deformed to position itself along a plane substantially normal to the drive shaft 38, and to expand the gap G. In this state, an edge portion 35a at the outermost circumference of the stationary thrust receiving face 35, as located at the rear side, and an edge portion 37a at the innermost circumference of the movable thrust receiving face 37 come into local contact with the elastic thrust races 34a and 34b of the rear thrust bearing 34.
During rotation of the swash plate 30 as the compression reaction force on the piston reverses, as described above, two alternating states are generated i.e. the state in which the paired thrust bearings are in face to face (contiguous) contact with the corresponding thrust receiving faces, and the state in which the same are in local (non contiguous) contact. At the time of the face to face contact, the contacting area of the two will increase to prevent partial wear. In the local contact, however, the thrust races 34a and 34b are partially worn, depending on the material of the thrust races. This partial wear shortens the lifetime of the thrust races and deteriorates the function of the thrust bearings and accordingly the elastic responsiveness of the same. As a result the compressor experiences increasing vibration and noise.